This invention relates to electrochemical oxidation decomposition of difficult to decompose substances such as aromatic compounds (benzene, chlorobenzene, chlorophenol) that are contained in things such as waste fluid of things such as developing waste fluids, incinerator exhaust gas treatment water, industrial waste water, landfill soil seeped waste water, organic compounds (such as trichloroethylene, tetrachloroethylene, tetrachloroethane), agricultural chemicals (such as DDT, PCP, parathion, TPN.tetrachloroisophthalonitril, triforin, MEP.sumithion, diazinon), dioxin, PCB's, water soluble polymers such as poly(vinyl alcohol), polyacrylonitrile, polyether) and nitrate ions.